Stille Reaction

by James

Description: The Stille reaction is a cross-coupling reaction using catalytic palladium that joins together alkenyl halides with organostannanes (organotin compounds).

1-headerNotes: The alkenyl halide can be Br, I, OTf, or occasionally Cl. The organostannane is usually Bu3Sn attached to an alkenyl or aryl group. A typical palladium catalyst is Pd(PPh3)4, although others can be used.

Because organotin compounds tend to be quite toxic, the Stille reaction is losing favour relative to the Suzuki reaction. It still finds a place in complex molecule synthesis, however, because the conditions are extremely mild.



Notes:  Like the Suzuki reaction, the Stille reaction is stereospecific. Note how in example 2, using an organostannane produces an E product, whereas using a Z organostannane (example 3) produces a Z product.

Mechanism: This is a cross-coupling reaction and full understanding requires concepts from inorganic chemistry that probably haven’t been taught to you yet.

This reaction proceeds in three key steps. After Pd(PPh3)4 loses two equivalents of PPh3 to form Pd(PPh3)2, oxidative addition (Step 1) to the alkenyl halide produces a palladium (II) compound. Next, transmetallation with the organostannane produces Bu3SnX [where X here is Br] and the palladium (II) complex containing two different carbon compounds. Finally, reductive elimination (Step 3) leads to formation of the key C-C bond, and regeneration of Pd(0), which then can perform a second catalytic cycle.



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